OFFSET
1,2
EXAMPLE
The largest integer which is <= 12 and does not occur among the first 11 terms of the sequence is 9. So a(12) = 12 + 9 = 21.
MATHEMATICA
f[l_List] := Block[{n = Length[l] + 1, k = n}, While[MemberQ[l, k], k-- ]; Append[l, n + k]]; Nest[f, {1}, 70] (* Ray Chandler, Sep 30 2006 *)
PROG
(PARI) {my(m=66, w=vector(2*m), a); print1(a=1, ", "); for(n=2, m, my(k=n); while(w[k], k--); print1(a=n+k, ", "); w[a]=1)} \\ Klaus Brockhaus, Oct 05 2006
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Sep 27 2006
EXTENSIONS
Extended by Ray Chandler and Klaus Brockhaus, Sep 30 2006
STATUS
approved